It is generally known that for the operation of an internal combustion engine, it is usual that mixture preparation equipment forms an air/fuel mixture outside of the combustion chamber of the engine. The mixture is drawn in by suction by a downward moving piston and flows into the combustion chamber. The mixture, which has flowed in, is compressed by the upwardly moving piston and is ignited. The combustion heat released in this manner increases the pressure of the precompressed gas. This combustion pressure is increased with respect to the precompressing pressure and supplies mechanical work via the piston and the crankshaft.
After each combustion stroke, the piston discharges the burnt gases as exhaust gases and then draws a fresh air/fuel mixture into the combustion chamber via suction. This gas exchange takes place in accordance with the four-stroke principle. In this way, a work operation takes place in two crankshaft rotations.
At this point, it is noted that the arrangement according to the invention is however not limited to a four-stroke spark-ignition engine. Indeed, it is also suitable for diesel and Wankel engines as well as for other internal combustion engines.
The physical characteristics and the chemical composition of the exhaust gases of the engine permit conclusions to be drawn with respect to several of the operating characteristic variables of the engine such as engine speed, fuel composition, air/fuel ratio, exhaust gas temperature and the like.
U.S. Pat. No. 3,908,167 discloses an arrangement for measuring an operating characteristic variable, namely the engine speed, of an internal combustion engine by evaluating a variable of the exhaust gas. In this arrangement, the evaluation of a light signal which changes because of the exhaust gases is used to operate on the engine speed.
A sensor suitable for this purpose includes means which can emit light, receive light and convert the light signal into electrical signals. The exhaust gas is conducted between the light source and the light receiver. This type of sensor is however quite complex.
It is also generally known to control the air/fuel mixture for an internal combustion engine by means of an exhaust gas probe which supplies a signal corresponding to the content of one gas component (oxygen) of the exhaust gas and this permits conclusions to be drawn as to the air/fuel mixture supplied to the engine.
U.S. Pat. No. 5,140,535, discloses a system which linearizes the signal of an oxygen probe with a voltage jump in the measuring range concerned and thereby makes possible an indication of the oxygen content in the exhaust gas and of the lambda values which are a direct measure for the air/fuel mixture supplied to the engine.
U.S. Pat. No. 4,452,079 and published German patent application DE-OS 38 04 680 disclose that it is also known to determine the speed of an engine by evaluating acoustic signals which emanate from the engine.
In contrast to the above, the requirement is present to detect and evaluate several variables caused by the exhaust gases which can be utilized to draw conclusions with respect to operating characteristic variables of the engine.
Published Japanese patent application 52-123 292 discloses an oxygen sensor which includes a solid electrolyte and a thermo element as a single unit.
However, no system is known wherein several operating characteristic variables of an engine can be determined by means of a single exhaust gas sensor.